The present invention generally relates to a keyboard interface implemented in an integrated circuit for interfacing either first or second external keyboards of different types to a central processing unit. The present invention more particularly relates to such a keyboard interface wherein the integrated circuit includes a set of terminals adapted to be coupled to either the first or second type of keyboard, and selectable first and second keyboard logic for supporting either the first or second type of keyboard at the set of integrated circuit terminals.
Keyboards are used in many applications for inputting data into a system. One such application is in personal computer systems which include a central processing unit and wherein a peripheral keyboard is used to input data onto the central processing unit controlled system data bus.
Two popular keyboards commonly used are referred to in the art as an AT type and an XT type. The AT and XT type of keyboards are very different.
The AT type keyboard is arranged to function with an associated 8042 microcontroller keyboard interface which requires its own set of control signals from the system in which the AT type keyboard is used. The 8042 microcontroller is also arranged to provide data generated from the AT type in an 8-bit parallel format which is buffered and then placed directly onto the data bus of the system.
The XT type keyboard is generally less expensive than the AT type keyboard. It also has its own interface which requires its own set of control signals from the system in which the XT type keyboard is used. In contrast to the AT type keyboard and associated 8042 interface, the XT type keyboard and the associated interface provide data generated by the keyboard in serial-bit format. The system in which such a keyboard is utilized, must therefore include the functionality of converting the serial-bit data to 8-bit parallel-bit data and placing the parallel-bit data onto the data bus of the system.
In systems wherein keyboards are required, it would be advantageous to provide the system user with the flexibility of being able to use either type of keyboard. Unfortunately, in the past, their functionality has not been provided. Also, in systems, such as personal computer systems, wherein integrated circuits are utilized, it would be advantageous to provide this functionality within an integrated circuit while utilizing the same set of integrated circuit terminal pins for supporting either type of keyboard.